The reactions of H<SUB>2</SUB>S and COS with high purity (99.9&37 ) and doped (Ca, Cd, Cu, Ni, Na and Pd) zinc oxide absorbents were investigated using batch recycle and plug flow reactors and using DRIFTS. The absorbents were characterised by BET surface area measurement, scanning electron microscopy, thermal decomposition and atomic absorption elemental analysis. High purity ZnO was also characterised by the 1R studies of adsorption of H<SUB>2</SUB>O, CO<SUB>2</SUB> and O<SUB>2</SUB>. The reaction between ZnO and H<SUB>2</SUB>S is structure sensitive. The sulphiding mainly takes place on the Zn-polar and O-polar faces of ZnO and proceeds to its bulk through a continuous rearangement and replenishment of hydroxyls due to H<SUB>2</SUB>O on these polar faces. The surface reaction takes place in two steps; first S-H groups form on the surface and then these groups are converted into surface sulphide where the first step is fast. The second step is slow in the absence of excess H<SUB>2</SUB>O. The reaction pattern is such that the initial reaction is fast where the solid's consumption varies from 4 to 35% depending upon the pre-treatment conditions of the absorbent such as temperature and atmosphere of calcining, water saturation, etc. Doping ZnO with Cd, Co and Cu improves its sulphiding capacity and rate compared to the high purity ZnO whereas doping with Na and Ca inhibits the sulphiding. The dopants directly affect the reaction on the polar faces as well as the bulk of the solid and affect the ZnO crystallite morphology. The effect of the presence of O<SUB>2</SUB> and CO<SUB>2</SUB> in the reactant H<SUB>2</SUB>S stream on the ZnO sulphiding performance was also investigated. The possible bulk reaction mechanisms were proposed.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:662239 |
| Date | January 1992 |
| Creators | Sohail, Khalid |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/14440 |
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